ORTHOPEDIC CASTS

Abstract: Heat-recoverable orthopedic casts include a support which is maintained in an elastically deformed condition by a casting polymer, e.g. a polycaprolactone (PCL) or a side chain crystallizable polymer having a relatively low melting point. The cast is placed around the limb and is then heated. The casting polymer softens and the cast recovers around the limb. A liner is preferably placed between the cast and the limb, especially when the casting polymer is PCL or has a comparable or higher melting point. For high strength casts, the support is preferably an open-mesh knitted fabric which, when fully relaxed, contains at most 300 holes per inch<2> (at most 45 holes per cm<2>). Such a fabric, when it is extensible to a maximum of 15 to 40 %, is also useful as casting tape which comprises a curable polymer casting composition, e.g. a water-curable polyurethane prepolymer. As illustrated in Figures 1 and 2, a stockinette liner (2) is preferably placed between the cast (1) and the limb as a thermal barrier. A reinforcing component may be used to strengthen the recovered cast. Suitable reinforcing components include (A) polyurethane precursors which are applied to the cast before or after recovery, and are polymerized during or after recovery, and (B) thermoplastic materials which are applied hot to the recovered cast. Casts made in this way can be divided to make splints which can be easily removed and replaced.

Description: ORTHOPEDIC CASTS CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of, and claims priority under the International Convention from, copending, commonly assigned U.S. Patent Application Serial No. 08/150,683 filed November 9, 1993, by Larson, Bitler, Greene, and Taft (Docket No. 9218-2US) and is also a continuation-in-part of copending, commonly assigned U.S. Patent Application Serial No. 08/092,351, filed July 14, 1993, by Stewart, Yoon, Larson, Ross, Greene, Kamp and Schmitt (Docket No. 9218.1), each of which is a continuation-in-part of Patent Application Serial No. 07/875,776 filed April 29, 1992, by Stewart, Larson and Yoon, now abandoned (Docket No. 9218). This application is also related to International Application No. PCT/US93/03962 filed April 28, 1993, claiming priority from U.S. Serial No. 07/875,776 (Docket No. 9218.1-PCT). The disclosure of each of those four applications is incorporated herein by reference. BACKGROUND OF THE INVENTION This invention relates to orthopedic casts. It is well known to make orthopedic casts, splints, supports, braces, shields, sheets, tapes, wound covers, and like orthopedic devices (all of which are referred to herein simply as "casts") from calcined gypsum (Plaster of Paris), from a polymer which is formed into shape while hot and hardens on cooling, or from a prepolymer which is formed into shape and then polymerized in situ, e.g. a polyurethane prepolymer which is hardened by water. The term "casting composition" is used herein to denote a polymeric composition which can be formed into shape around a substrate (referred to herein simply as a limb) and then hardened by chemical reaction or by cooling. Known casting compositions can comprise a single polymer or a mixture of two or more polymers, and can contain additional ingredients such as inorganic fillers,and can be associated with a flexible support, which may have some elasticity, for example a fabric or a foam sheet. Reference may be made for example to US Patent Nos. 3,692,023 (Phillips), 3,728,206 (Buese), 3,809,600 (Larson), 4,019,505 (Wartman), 4,105,025 (Wang), 4,193,295 (Gruber), 4,231,356 (Usukura), 4,273,115 (Holland), 4,326,509 (Usukura), 4,404,333 (Watanabe), 4,427,002 (Baron), 4,433,680 (Yoon), 4,502,479 (Garwood), 4,770,299 (Parker), 4,473,671 (Green), 4,483,333 (Wartman), 4,609,578 (Reed), 4,627,424 (Baron), 4,643,909 (Kammerer), 4,661,535 (Borroff), 4,668,563 (Buese), 4,784,123 (Robeson), 4,912,174 (Grouiller), 4,937,145 (Dull), 4,946,726 (Sandvig), 4,951,656 (Gorka), 4,984,566 (Sekine), 5,014,403 (Buese), and 5,027,804 (Forsyth), European Patent Publication Nos. 0086686, 0110860, 0169037, 0338815 and 0358451, and PCT Publication Nos. WO 90/14060 and 91/09909. The disclosure of each of those documents is incorporated herein by reference. All the known methods of making casts require excessive time, skill and care for good results. Prepolymers offer advantages over Plaster of Paris, but the use of water is messy and inconvenient, and frequently results in undesirable wetting of bandages and cast linings. Thermoplastic compositions avoid the use of water, but they have not so far proved satisfactory in use. When using casts which include an elastic support, the practice has been to stretch the cast as it is wrapped around the patient; this leads to variable results, with excessive and/or insufficient pressure, even when very skillfully applied. The related U.S. application Nos. 08/092,351 and 07/875,776 and International Application No. PCT/US93/03962 (none of which had been published at the priority date of November 9, 1993 claimed by this International application) describe novel casts, novel thermoplastic casting compositions, and novel measures for obtaining improved results with thermoplastic casting compositions in general. In preferred embodiments, these related applications describe novel heat-shrinkable casts comprising a support which is held in an elastically stretched state by a thermoplastic casting composition, and the application of such a cast by placing it around a patient, and then heating it in situ, preferably by means of hot air, thus softening the casting composition and permitting the cast to shrink towards the patient SUMMARY OF THE INVENTION In the further development of heat-recoverable casts as described in the related applications, we have discovered, in accordance with a first aspect of the present invention, that if a flexible interior member (referred to herein as a liner) is placed between the patient and the cast while the heat-recoverable member is being heated, it provides a thermal barrier which increases the maximum temperature which the casting composition can reach during the application of the cast, and thus broadens the range of compositions which can be used without danger of harming the patient. For example, we have successfully used casting compositions containing polycaprolactone (PCL), even though PCL melts above the maximum temperature which can be tolerated by human patients. The presence of the liner also increases the reliability with which a satisfactory cast can be prepared. These benefits are particularly apparent when the liner includes padding material which is compressed during recovery of the cast We have also discovered, in accordance with a second aspect of the present invention, that the properties of a heat-recovered cast (whether or not it includes a liner as described above) can be further improved by providing a flexible reinforcing component on at least part of the cast and treating the component, during and/or after recovery of the cast, to make the component relatively rigid. The flexible component can be present on the heat-recoverable cast, in which case it preferably does not substantially impede recovery of the cast Alternatively or additionally, the flexible component can be applied to the cast after it has been recovered. The flexible component is preferably a prepolymer which is polymerized on the cast. The flexible component can also be a thermoplastic casting composition which (a) is applied hot to the outside of the recovered cast, or (b) is applied cold to the outside of the recovered cast and is then heated in place. For example, the flexible component can be a second heat-recoverable cast. When a flexible component is used in this way, the physical properties and the appearance of the finished composite cast depend on both the heat-recovered component and the hardened flexible component Indeed, the heat-recovered cast can serve primarily as a mold for the flexible component and make a relatively small contribution to the physical properties of the finished composite cast. We have also discovered, in accordance with a third aspect of the present invention, that when the support is a knitted fabric comprising at least one elastically extensible yarn, preferably an elastomeric yam, and at least one relatively inextensible yam, preferably a fiberglass or other high strength yarn, the size of the holes in the fabric has an important effect on the ease with which the cast can be recovered and the strength of the recovered cast For many types of cast, therefore, especially casts which are required to have high strength, it is preferred to use a fabric which has a relatively large mesh such that the fabric (in a fully relaxed state) has at most 300 holes per inch 2 (at most 45 holes per cm 2 ). When a cast is made by heating a heat-recoverable cast comprising an elastically deformed support and a heat-softenable casting composition, it is usually necessary, in order for the cast to have adequate strength, for the cast to have more than one thickness of the support. In principle, this can be achieved by recovering a single cast comprising multiple layers of the support, or by successive recovery of two or more casts, one on top of the other, each of the casts containing one or more supports. In practice, it is more convenient to use a single cast which is a laminate of two or more supports, each maintained in a stretched condition by the solid casting composition, because the cast can be preassembled at a manufacturing site and because multiple recovery steps, one after the other, are not required. On the other hand, the smaller the number of layers in a cast, the easier it is to recover the cast. In our earlier work, as disclosed in Application No. PCT/US93/03962, we found that when making a high strength cast, the best compromise was to use a two-layer cast (i.e. a cast made by assembling a laminate of two layers of heat-shrinkable fabric/polymer), and to apply a first two-layer cast around the limb, and then to apply a second two-layer cast around the recovered first cast. This procedure, and the resulting casts, show many improvements over the previously available techniques. However, we have now found that by increasing the open area of the support fabric, yet further improvements can be obtained, especially when making a high strength cast. For example, a three-layer cast (i.e. a cast made by laminating three layers of heat-shrinkable fabric/polymer) can be effectively recovered around a limb in a time which is not substantially longer than the time needed to recover a two-layer cast and a great deal shorter than the time needed to recover two two- layer casts previously employed, and provides a finished cast of comparable strength. We have also discovered, in accordance with a fourth aspect of this invention, that after shrinking down a heat-shrinkable cast comprising a support which is held in an elastically stretched state by a thermoplastic casting composition, the recovered cast can be converted into a removable splint by dividing it along one or more lines so that it can be removed from the limb, and securing one or more fasteners, e.g. straps, to the cast so that, after the cast has been removed from the limb (e.g. so that the limb can be inspected by a doctor), it can be re-placed around the limb and secured in position. The cast is preferably divided along a single line and then has sufficient flexibility to be opened up and removed from the limb. In many cases, the shrank cast can be easily cut by means of a pair of shears. The creation of a closely fitting and removable splint in this way provides great advantages over the techniques now available. We have also discovered, in accordance with a fifth aspect of this invention, that the open mesh fabrics used in the third aspect of the invention, particularly when they have a maximum elastic extensibility of 15 to 40%, preferably 20 to 35%, are also useful in casting tapes which are stretched as they are applied, the fabric being coated with a curable prepolymer composition, e.g. a water-curable polyurethane precursor, which is treated with a curing agent just before, or during, application of the casting tape. The term "curing agent" is used herein to include chemical curing agent and electromagnetic or other radiation which will cure the prepolymer. In the casts used in this invention which comprise a laminate of two or more supports, each maintained in a stretched condition by the casting composition, the layers are preferably separate from each other except for sufficient attachment to prevent their relative displacement during handling, especially when the cast is placed around a limb. Such attachment can be provided, for example, by a strip of hot melt adhesive which extends through the layers. The invention includes products and processes which make use of the various aspects of the invention, including combinations of any two, or three, or all four, of the first, second, third and fourth aspects of the invention, as well as combinations thereof with one or more other features disclosed in the related applications or in the prior documents incorporated herein by reference. The heat-recoverable articles used in the present invention are generally heat- shrinkable, and the supports therein correspondingly are generally elastically stretched. The invention is, therefore, chiefly described by reference to such articles. A first preferred embodiment of the present invention is an orthopedic cast which comprises ( 1 ) a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which comprises a casting polymer having a transition point T s , which contacts the support and maintains it in an elastically stretched condition, and which, when the cast is heated to a temperature above T s after it has been placed around a limb, softens and permits shrinkage of the heat-shrinkable member towards the limb, and (2) a liner which is secured to the inside of the main member and which, when the cast is heated after it has been placed around a limb, provides a thermal barrier between the limb and at least part of the main member. The term "transition point" is used herein to denote either a crystalline melting point (T m ) or a glass transition point (T g ). The term "soften" is used herein to denote softening of the casting polymer as it undergoes crystalline melting or as it passes through a glass transition. A second preferred embodiment of this invention is an orthopedic cast which comprises (1) a heat-shrinkable main member as defined in the first preferred embodiment of the invention, and (2) a flexible reinforcing component which is provided on at least a part of the main member and which can be subjected to a treatment which will reduce its flexibility. The cast optionally includes a Uner as required by the first preferred embodiment of the invention. A third preferred embodiment of the invention is a heat-shrinkable article which (1) is suitable for use as an orthopedic cast or can be converted into an article suitable for use as an orthopedic cast; (2) comprises (a) a knitted fabric support which (i) is in an elastically stretched condition, (ii) comprises at least one elastically stretched yam and at least one relatively inextensible yam, and (iii) when on its own in a fully relaxed state, has at most 300 holes per inch 2 (at most 45 holes per cm 2 ); and (b) a solid casting composition which (i) comprises a casting polymer having a transition point, T s , which is above 40°C, and (ϋ) contacts the support and maintains it in the elastically stretched condition, but does not fill the holes of the support; and (3) when heated above T s in the absence of any restraint, shrinks so that at least one dimension of the article decreases from a first value x to a second value y which is at most 0.95x, said shrinkage being due at least in part to elastic shrinkage of the elastically stretched yarn. A fourth preferred embodiment of this invention is a heat-shrinkable article which is suitable for use as an orthopedic cast in conjunction with a liner in accordance with the first aspect of the invention, or which can be converted into such a cast, and which comprises (a) an elastically stretched support, and (b) a casting composition which (i) comprises a casting polymer having a transition point T s , which is higher than can be tolerated by a patient in the absence of the liner, e.g. at least 55°C, optionally at least 60°C, e.g. 55° to 85°C or 55° to 65°C, preferably polycaprolactone, (ii) contacts the support and maintains it in an elastically stretched condition, and (iii) when the cast is heated to a temperature above T s after it has been placed around a limb, softens and permits shrinkage of the heat-shrinkable member towards the limb. A fifth preferred embodiment of the invention is a method of forming orthopedic casts around a limb, which method comprises (A) placing around the limb an article according to the first, second or third preferred embodiment of the invention which, when in position around the limb, has a closed cross-section (as defined below); and (B) heating the article so as to soften the casting composition and cause shrinkage of the heat-shrinkable article towards the limb. When the article includes a flexible, reinforcing component, the method includes subjecting the reinforcing component to a treatment which reduces its flexibility. The term "closed cross-section" is used herein to denote an article which, when viewed in cross section, substantially encloses an open area containing the limb and has a continuous or substantially continuous periphery such that shrinkage of the article conforms it to the general shape of the limb (around a liner and/or padding, if present). Thus the article is preferably in the form of a tube. A sixth preferred embodiment of the invention is a method of forming an orthopedic cast around a limb, which method comprises (A) placing around the limb an orthopedic cast which has a closed cross- section and which comprises a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which contacts the support and maintains it in an elastically stretched condition; (B) heating the orthopedic cast so as to soften the casting composition and cause shrinkage of the heat-shrinkable member towards the limb; and (C) subjecting a flexible reinforcing component on at least part of the main member to a treatment which reduces its flexibility, said treatment being carried out during step (B), or after step (B), or both. A seventh preferred embodiment of the invention is method of forming an orthopedic cast around a limb, which method comprises (A) placing around the limb an orthopedic cast which has a closed cross- section and which comprises a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which contacts the support and maintains it in an elastically stretched condition; (B) placing a liner between the cast and the limb; and (C) heating the orthopedic cast so as to soften the casting composition and cause shrinkage of the heat-shrinkable member towards the limb. In this embodiment of the invention, the liner can be secured to the cast (as in the first preferred embodiment) or can be placed around the limb before the cast. An eighth preferred embodiment of the invention is a method of making an orthopedic cast according to the second preferred embodiment of the invention, which method comprises (A) providing an elastically stretchable support; (B) contacting the support, while it is elastically stretched, with a casting composition which comprises a casting polymer having a transition point T s and which is at a temperature above T s ; (C) cooling the casting composition to a temperature below T s to produce a heat-shrinkable main member wherein the casting composition maintains the support in an elastically stretched condition; and (D) providing on the main member a flexible reinforcing component which can be subjected to a treatment which will reduce its flexibility. In this method, the hot casting composition is preferably applied to the support while it is elastically stretched, e.g. between rollers or over a form. However, it is also possible to apply the casting composition to the support while the support is in its relaxed state, and then to stretch the coated support, with heating before, during or after the stretching. The reinforcing component can be provided at any convenient stage. For example, it can be placed on the support before or after the support is elastically stretched; it can be applied before or after the casting composition, or be a part of the casting composition; it can be provided on all or on selected part(s) of the main member, including parts which are not contacted by the casting composition; and it can be present as a continuous or intermittent coating or as a separate, e.g. a self-supporting, film. The support can be a sheet or a tape, but in the final product is preferably of closed cross-section, particularly a tube, thus providing a cast of closed cross-section which can if desired be modified by cutting, e.g. to a desired shape or to provide a cast of open cross-section. Alternatively, the support can be a sheet or a tape which is formed into a cast of closed cross-section at any convenient stage of the process. For example, a heat-recoverable sheet or tape can be wrapped around a form and the outer end secured to the wrapped material beneath it. The reinforcing component can be provided on the sheet or tape before it is wrapped, or as it is wrapped, or after it has been wrapped. A ninth preferred embodiment of the invention is a method of making a removable splint which comprises (A) placing around the limb an orthopedic cast which has a closed cross- section and which comprises a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which contacts the support and maintains it in an elastically stretched condition; (B) heating the orthopedic cast so as to soften the casting composition and cause shrinkage of the heat-shrinkable member towards the limb; (C) after the cast has cooled, dividing it along one or more lines so that it can be removed from the limb; and (D) securing fasteners to the cast so that the cast, after it has been removed from the limb, can be replaced and secured around the limb. The fasteners are typically straps which are secured to the cast by means of, for example, a hot melt adhesive, preferably through a patch which comprises a fabric support and a hot melt adhesive and which is sewn to the strap; the hot melt adhesive is preferably the same as the casting polymer. A tenth preferred embodiment is a removable splint which comprises ( 1 ) a flexible polymeric cast which is divided along at least one line so it can be placed over and removed from a limb, said cast comprising a fabric support and thermoplastic polymer contacting the support, and (2) fasteners which can be used to secure the cast around a limb. An eleventh preferred embodiment of the invention is an article which is suitable for use as an orthopedic casting tape and which comprises (a) a knitted fabric support which (i) comprises at least one elastically extensible yam and at least one relatively inextensible yam (ii) when on its own in a fully relaxed state, has at most 300 holes per inch 2 (at most 45 holes per cm 2 ) and can be elastically extended in a lengthwise direction to an elastic limit at which its length is between 1.15 times and 1.4 times its fully relaxed length, and (b) a polymeric casting composition which contacts the support and which comprises a curable precursor for a polymer. A twelfth preferred embodiment of the invention is a method of forming an orthopedic cast around a limb which comprises (A) wrapping around the limb a casting tape according to the eleventh preferred embodiment of the invention while the casting composition is in a state which permits elastic extension of the support, and (B) treating the casting composition so that, after the casting tape has been wrapped around the limb, the composition hardens to form a relatively rigid cast. BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal cross-section of a cast according to the first preferred embodiment of the invention, Figure 2 is a transverse cross-section on line LI-II of Figure 1, and Figure 3 is a plan view of a flattened heat-recoverable main member. DETAILED DESCRIPTION OF THE INVENTION Definitions. Abbreviations and Measurements In this specification, parts, amounts and percentages are by weight. Temperatures are in °C. Molecular weights are weight average molecular weights expressed in Daltons and are determined by gel permeation chromatography (GPC) in tetrahydrofuran (THF). First order transition points (often referred to as melting points), glass transition points, and heats of fusion are determined by a Differential Scanning Calorimeter (DSC) using the second heat cycle and a heating rate of 10°C/minute. The softening point, T m , for crystalline polymers is the peak of the DSC curve. Crystallization temperatures are determined by a DSC at a cooling rate of 10°C/minute. The "power" of a material is defined as the force in pounds required to stretch a 1 inch (2.54 cm) wide sample of the material to twice its original length. Melt Index values are measured by ASTM D1238 (modified). Tensile modulus values are calculated according to ASTM D638 after testing the material by ASTM D 1708 at a crosshead speed of 1 inch/minute (2.54 cm/minute). Strength values given herein are the tensile modulus of the material (psi) multiplied by the thickness of the material (inch). Strength values for casts above T m are measured after heating the material to ( m +10)°C and allowing it to equilibrate at that temperature for 5 minutes. Strength values for molded casts are measured at 25°C.after heating the cast to at least (T m +10)°C, allowing the cast to recover without any restraint, cooling it to 25°C and allowing the cast to equiUbrate at 25°C for 1 hour. Air flow permeabiUty (AFP) values given herein are measured as follows. An air gun is secured in a jig, and an anemometer is placed in a reference position at the center of the air stream at a distance of 5 inch (12.7 cm) from the tip of the gun. The gun is adjusted so that the air is cold and the air flow recorded by the anemometer is about 1700 ft/rnin (570 m/min). A flat sample of the heat-recoverable member or the liner (or a corresponding sample — see below) in the shape of a circle 2 inch (5.1 cm) in diameter, or a larger sample, is placed across the air flow at right angles to the air flow, at a distance of 5 inch (13 cm) from the tip of the gun. The air flow is recorded by the anemometer at three different spots within about 0.5 inch (1.2 cm) of the reference position, and is averaged. The AFP of the cast is the average air flow, expressed as a percentage of the air flow without the cast. Since the sample must be flat, and the heat-recoverable member, both before and after molding, is usually not flat, it is usuaUy necessary to measure AFP values on corresponding samples, i.e. on sheets obtained by flattening out a portion of the cast, taking care not to change its porosity, or on sheets which are flat but which have otherwise been prepared in the same way as the heat-recoverable member. For example, after measuring the AFP of an unused sample using cold air, the air gun can be adjusted to provide hot air which wiU effect recovery of the sample, and the AFP of the recovered sample can be measured. Crush strengths are measured on an Instron 1122 tensile tester by placing the product between the plates of a crushing jig and forcing the plates together at room temperature. Casting Polymers First to Tenth Embodiments The casting compositions used in the first to tenth embodiments of this invention contain a casting polymer having a transition point T s , preferably a crystalline melting point (T m ), of at least 40°C, particularly at least 45°C, especially at least 48°C, to ensure that the cast does not soften under normal atmospheric conditions. T s should also be such that the casting polymer will soften and permit recovery at temperatures which do not cause distress to human patients. When the cast includes a Uner which acts as a thermal barrier to the heat appUed to the cast to cause its recovery, T s can be for example as high as 85°C, but is preferably not more than 70°C. When no such Uner is present, T s is preferably no more than 60°C, particularly no more than 55°C. Softening preferably takes place over a range of less than 20°C, particularly less than 15°C, especially less than 10°C, more especially less than 5°C. If the casting polymer is a polyolefin, it preferably consists essentially of a single tactic form, i.e. is whoUy atactic or syndiotactic or isotactic, so that its melting point is sharp. It is preferred that rehardening should take place rapidly on cooUng from above T s to below T s , so that the patient does not have to remain still for an extended time whUe the cast hardens; we have found that excellent results are obtained in practice if, when the cast is heated above T s and then cooled to (T s - 10)°C at a rate of 10°C/min, the casting polymer rehardens in not more than 2 minutes, preferably not more than 1 minute, after it has cooled to T s . When a liner is used, casting polymers having T s 's above 55°C, e.g. polycaprolactone-based compositions, can be used without causing distress to the patient, and are often preferred because of their ready availabiUty. Suitable polycaprolactone- based casting polymers include compositions disclosed in the documents incorporated herein by reference. The polycaprolactone preferably has a T m of about 55°C to about 60°C, and a molecular weight of 20,000 to 80,000, particularly 30,000 to 40,000. Examples of such polycaprolactones which are commerciaUy available include the product sold by Solvay Interox Chemicals (Waπington, Great Britain) under the trade name CAPA-640, which has a reported molecular weight of about 37,000 and a Tm of about 57°C, and the product sold by Union Carbide (Danbury, Connecticut, USA) under the trade name Tone 767E, which has a reported molecular weight of about 40,000 and a T m of about 55°C. Polycaprolactones of molecular weight less than 40,000 are generally preferred because of their lower melt viscosity. Also useful as casting polymers in the present invention, particularly when the heat- recoverable cast does not include a liner, are crystalline polymers in which the crystallinity results exclusively or predominantly from side chains which are attached to the polymer backbone. Such polymers are often referred to as side chain crystaUizable polymers, or SCC's, and are described in detail in the three copending applications referred to above and in International Patent AppUcation No. PCT/US92/08508 filed October 6, 1992 (Docket No. 9213.2-PCT) and copending commonly assigned US Application Serial No. 08/048,280 (Docket No. 9213.2) filed April 14, 1993, the disclosures of which are incorporated herein by reference and to which reference may be made for further details. The SCC polymers can be mixed with other polymers, including for example polycaprolactone, ethylene/vinyl acetate copolymers, ethylene/butyl acrylate copolymers and ethylene/methyl acrylate copolymers. The molecular weight of the SCC casting polymer is generally more than 5,000, and when it is the sole polymeric ingredient of the casting composition is preferably at least 50,000, for example 60,000 to 300,000, particularly at least 100,000, for example 140,000 to 200,000. When the casting polymer is a block copolymer containing SCC blocks, its molecular weight is preferably more than 25,000, especially more than 75,000, with the molecular weight of each SCC block preferably being 2,500 to 20,000. The casting polymer can be crosslinked by radiation or chemical crosslinking methods known to those skilled in the art. Radiation crosslinking can be effected, for example, by an electron beam or Cobalt 60 radiation. Chemical crossUnking can be effected, for example, by means of peroxides or silanes, by ionic crosslinking, or with the aid of multifunctional agents. Eleventh and Twelfth Embodiments The eleventh and twelfth embodiments of the invention use casting compositions which comprise a curable polymeric composition, preferably a water-curable polyurethane precursor, for example a composition as described in one of the documents incorporated herein by reference. Casting Compositions The casting composition can contain, in addition to the casting polymer, one or more additional polymers and/or one or more non-polymeric ingredients, e.g. inorganic fillers, plasticizers, antioxidants, processing aids, and pigments, for example carbon black, graphite, glass fibers, Kevlar fibers, silica, titanium dioxide, talc, magnesium carbonate and calcium carbonate. For further detaUs, reference may be made to the five copending appUcations referred to above. Supports First to Tenth Embodiments The supports used in the first to tenth embodiments of the present invention are preferably elastically deformable. The support preferably has, in the main member before it is recovered, an open structure which assists in the heat transfer between different parts of the main member, and which, in the finished cast, remains sufficiently porous to ensure that the support has a high moisture vapor transmission rate (MVTR) and thus does not prevent the limb from "breathing". Particularly for making high strength casts, e.g. load-bearing casts, casts around broken bones, etc., we have obtained exceUent results using a fabric support which contains at most 300 holes per inch 2 (at most 45 holes per cm 2 ), particularly 50 to 25, especially 80 to 150, holes per inch 2 (8 to 40, preferably 12 to 25, holes per cm 2 ). However, for cases where less strength is adequate or is desired, e.g. around sprained limbs, soft tissue injuries, carpal tunnel injuries, greenstick fractures, and fractures which are mostly healed, supports having a greater number of holes, e.g. 300 to 600 holes per inch 2 (45 to 90 holes per cm 2 ) may be preferred. Preferred supports are knitted fabrics (preferably warp- knitted, especially Raschel knitted, fabrics) which comprise one or more elastomeric yams and one or more high strength yams, particularly glass fiber yams. The yams in the fabric preferably consist essentially of continuous filaments which are free from permanent crimps and have a diameter of 0.007 to 0.02 inch (0.018 to 0.05 cm). The support may be isotropic or have elasticity or other properties which vary directionaUy. Preferably the support can be stretched elastically in at least one direction by at least 25%, preferably at least 50%, e.g. 50 to 225%, based on the corresponding dimension of the support in its unstretched state, i.e. to at least 1.25 times, preferably at least 1.5 times, e.g. 1.5 to 3.25 times, its original dimension. The power of the fabric is preferably 0.1 to 2.0 lb/inch (18 to 360 g/cm), and the fabric may contain for example 5 to 40%, preferably 10 to 25%, of the extensible yam to provide suitable recovery forces. Eleventh and Twelfth Embodiments The knitted support fabrics used in the first to tenth embodiments are also useful in the eleventh and twelfth embodiments providing that they are elastically extensible to an elastic Umit of 15 to 40%, preferably 20 to 35%. If the extensibiUty is too low, the tape will not conform to the limb as the tape is wrapped; if the extensibiUty is too high, there is a danger that the tape will be wrapped too tightly around the limb so that the hardened cast will cause distress to the patient. Heat-Recoverable Main Members The casts used in this invention, before they are recovered around a substrate, preferably comprise a heat-recoverable main member whose heat-recoverabUity results at least in part from the presence of an elastomeric support which is maintained in an elastically deformed (usually stretched) condition by the casting composition, and which recovers towards an undeformed configuration when the casting polymer is softened by heating. The casts wiU often comprise two layers, each layer comprising a support maintained in an elasticaUy stretched condition by a casting composition. The layers may be the same or different, and are optionaUy bonded together. The available recovery of the main member wiU depend on the extent of the deformation put into the support. Preferably the main member, if heated in the absence of any restraint, will recover so that at least one dimension thereof decreases from a first value x to a second value y, where y is at most 0.95x, particularly at most 0.75.*. It is generally unnecessary for y to be less than OΛx, and in most cases y is more than 0.45 The strength (including the crush strength) of the recovered main member depends not only on the support and the casting polymer and the dimensions and amounts thereof, but also on the extent of the recovery and the heating used. It is often desirable to continue the heating for a short while after recovery of the main member, e.g. for another 1 to 3 minutes, in order to consolidate the cast. The recovery forces in the main member should be sufficient to ensure adequate conformance of the cast to the limb, but not so high as to damage the patient, or cause pain, or reduce blood flow. The power of the cast , in the direction of recovery, is, therefore, preferably 0.1 to 2.0 lb mch (18 to 360 g/cm). We have found that the casts are much easier to apply, without overheating which can cause distress to the patient or the orthopedist, if the main member has, before recovery, an open structure which permits rapid and uniform heating of the casting composition, especiaUy when using a hot air gun to heat the cast. Thus the main member, before recovery, preferably contains a pluraUty of apertures having an average area of at least 0.01 cm 2 , preferably at least 0.02 cm 2 ; on the other hand, the apertures should not be so large as to permit the limb to become overheated. EspeciaUy when the cast includes a liner, the size of the apertures is preferably less than 0.12 cm 2 , e.g. 0.03 to 0.12 cm 2 , particularly 0.03 to 0.09 cm 2 . When no liner is present, the size of the apertures is preferably less than 0.08 cm 2 , particularly less than 0.06 cm 2 . In the heat-recoverable article, the number of holes (which is of course dependent on the number of holes in the relaxed support and the extent to which the support has been stretched) is preferably 20 to 100, particularly 30 to 60, holes per inch 2 (3 to 15, particularly 5 to 10, holes per cm 2 ) when making high strength casts, but may be higher, e.g. 100 to 170 holes per inch 2 (15 to 25 holes per cm 2 ) when making relatively low strength products. The size and number of the apertures are preferably such that over substantial areas of the heat-recoverable member, particularly over the whole of the casting polymer, heating the cast with a hot air gun causes a difference in temperature, between the inside and the outside of the heat- recoverable member at any particular point, of not more than 15°C. Preferably the main member has, before recovery, an air flow permeabUity (AFP) of at least 5%, more preferably at least 10%, particularly at least 20%, but less than 60% when a liner is present, and less than 45% when no liner is present, more preferably less than 35%. The AFP of the heat-recovered member, after recovery, is preferably at least 1 %, more preferably at least 2%, particularly at least 5%, especiaUy at least 8%, but is preferably less than 25%, more preferably less than 20%, particularly less than 15%, especially less than 10%. It is desirable that the cast should become relatively inflexible in a short period after molding is complete. Preferably, therefore, the casting composition, as it cools, changes from a moldable composition to a relatively stiff composition over a temperature range of less than 10°C, particularly less than 5°C, and preferably does so in less than 5 minutes, particularly less than 2 minutes. The casting polymer need not recover all of its crystalUnity in order for the casting composition to become relatively inflexible. In this specification, the polymer can be regarded as having cooled to a crystalline relatively inflexible material if its crystaUinity is at least 0.5 X, where X is the crystaUinity of the polymer after it has been cooled from above T m to (T m -10)°C and maintained at (T m - 10)°C for four crystaUization half Uves. The main member preferably has a closed cross-section which is in approximately the desired final shape, but sufficiently oversize to allow the cast to be placed around the limb. However, to assist in fitting a cast to a limb, and/or to assist in its later removal, the cast may comprise at least one elastomeric component which is free of the casting composition and is elasticaUy deformable before or after (preferably both before and after) the cast has been fitted around the substrate. The elastomeric component can be a longitudinal component which extends over part or aU of the length of the cast, or a radial component which extends around part or all of the circumference of the cast. For further details, reference should be made to US appUcation Serial No. 08/092,351, incorporated by reference herein. In addition, it should be understood that the invention also includes heat- recoverable articles, e.g. tapes, which can be used to make heat-recoverable casts of closed cross-section, e.g. by wrapping around a form to make a preformed cast or by wrapping around the Umb itself. Pre-shaped casts may have a wide variety of shapes, including for example a cyUnder for use as a finger splint, a bent cylinder to surround an ankle, knee or elbow, or a glove to surround part or all of a hand. Preparation of Casting Compositions and Heat-Recoverable Main Members The casting compositions used in this invention can be prepared by procedures well known in the art, and can be formed or applied to supports by procedures well known in the art, e.g. as solutions in organic solvents which are removed by drying, or as molten compositions, e.g. by melt extrusion onto the support or by hot lamination. When the composition is applied as a melt, it preferably has a viscosity at 95°C and/or at the temperature at which it is applied, of 700 to 7,000 poise, preferably 1500 to 7000 poise. The casting composition is preferably applied to the stretched support and then cooled while maintaining the support in the stretched condition. However, it is also possible to apply the casting composition to the non-deformed support, and then to stretch the composite, e.g. over a mandrel or other form, whUe the casting composition is at a temperature above T s , followed by cooling with the support in its stretched condition. Casts having similar shape but different strengths can readUy be prepared by wrapping a cooled, coated, stretched tape over a form twice, or three times, or more than three times. GeneraUy at least one dimension of the support is stretched by 40 to 150% of its unstretched length (i.e. to 1.4 to 2.5 times its unstretched length), preferably 60 to 150%, for example 100 to 140%, of its unstretched length. After the composition has been applied to a support, it may be desirable to heat it, at a temperature above T s , optionally with pressure, to ensure that it fully penetrates the support The casting composition is preferably applied in a way and in amount such that it does not block the holes in the support, and preferably so that the average area of the holes in the cooled, coated, heat-recoverable product is at least 0.5 times, particularly at least 0.7 times, especially at least 0.8 times, the area of the holes in the stretched support before it is coated. For this purpose, it may be desirable to blow air through the casting composition to ensure that the open structure of a porous support is not fiUed up by the casting polymer. The casting composition generally provides 40 to 60% by weight of the heat-recoverable article. In many cases it is desirable that the heat-recoverable main member should be sufficiently flexible to be flattened, e.g. for ease of storage or to enable it to be cut to a desired shape. Liners When a liner is present, as is preferred, the liner provides a thermal barrier between the limb and at least part, preferably all, of the heat-recoverable main member while the main member is being recovered. Since the Uner remains in place between the recovered cast and the Umb, it must have satisfactory properties (e.g. permeabmty to water vapor) for this use. In the cast before it is recovered, the Uner is preferably elasticaUy deformed so that it fits snugly around the limb after the cast has been recovered. We have obtained excellent results with a Uner which is elasticaUy deformable and which has a pluraUty of apertures through its thickness such that it has an air flow permeabUity (in the undeformed state) of less than 25%. When, as is preferred, the main member has a plurality of apertures through its thickness, so that it can be more readily recovered by means of a stream of hot air, the liner preferably has an air flow permeabiUty of less than 0.75 times the air flow permeabiUty of the main member. The liner preferably comprises a stockinette fabric, i.e. an elastically deformable circular knit fabric, preferably a circular rib knit fabric. The stockinette may for example comprise a natural or synthetic polymeric yam, e.g. a cotton or other cellulosic yam, or a polyester, polyamide or polypropylene yam. The stockinette preferably has a fully recovered diameter which enables it to fit snugly around the limb to which the cast is applied. Suitable stockinette fabrics are well known in the art, for example for covering a Umb before forming a cast around the Umb. In the present invention, by contrast, the liner is secured to the main member so that it provides a thermal barrier between the limb and the heat-recoverable main member. The liner is preferably secured to the main member by means of end sections which pass around the ends of the main member and are secured to the outside of the main member, preferably by means of elastic forces generated by deforming the Uner. While the heat-recoverable main member is being heated in order to recover it, the ends of the Uner are preferably unfolded so that they cover the parts of the patient adjacent to the area to be covered by the cast, thus providing a thermal barrier in these areas as well as underneath the cast The liner preferably comprises a padding material which is compressed between the limb and heat-recovered main member. Particularly when such padding material is present, a uniform pressure between the cast and the Umb can reacUly be achieved. Suitable padding materials are typicaUy non-woven fabrics of cotton (or other cellulosic) or synthetic, e.g. acryUc or polyester, fibers, and are well known to those skiUed in the art. Foamed polymers can also be used as padding material. Materials which combine an elasticaUy deformable fabric and padding material are commercially available and can be used in this invention, including for example the product sold by Landec Corporation under the trade name CastUner, which has a knitted outer ply containing polyester and Lycra fibers and a terry loop inner ply also containing polyester and Lycra fibers; the product sold by Smith and Nephew Casting under the trade name ProTouch One-Step, which is a cotton/spandex stockinette having adhesively bonded to it polyester padding which permits the stockinette to expand without tearing the padding; the product sold by Balfour Health Care under the trade name Terry Rolls, which is an acrylic/spandex rib knit stockinette with acryUc loops on one surface only; and the product sold by Knit Rite under the trade name Cast-Rite, which is a thick acrylic/spandex circular knit stockinette fleeced on one surface only. Reinforcing Components In preferred embodiments of the invention, a flexible reinforcing component is provided on at least part of the heat-recoverable member, and is treated to reduce its flexibiUty whUe the main member is being recovered, and/or after the main member has been recovered. The treatment wiU generally not affect the main member, but the invention includes reinforcing components and treatments which have separate effects on the reinforcing component and on the member and those which act jointly on the reinforcing component and the main member to strengthen the finished cast. The flexible component can be appUed to the main member at any appropriate stage, for example before the main member is stretched at aU, after it has been stretched but before the casting polymer has been applied to it, while it is heat-recoverable (either as a heat-recoverable tape or as an article made by wrapping a heat-recoverable tape around a form), while it is being heat-recovered, or after it has been heat-recovered. There may be more than one reinforcing component, applied to the same or different parts of the main member, appUed at the same or different stages, and consisting of the same or different materials. When the reinforcing component is appUed to the main member before the main member is recovered, it must not prevent, and preferably does not substantially change, recovery of the main member. Preferably it comprises a prepolymer (i.e. a mixture of monomers and/or oUgomers which can be polymerized), and which can be treated, during and/or after recovery of the main member, to effect polymerization. The prepolymer can for example be appUed as such or as part of a Uquid composition, for example a solution of the prepolymer in a solvent which is at least partiaUy evaporated before and/or during recovery of the main member. The prepolymer can also be applied in association with a substrate, e.g. a knitted, woven or non- woven fabric or netting, a polymeric film, or reinforcing fibers, provided that the substrate does not prevent recovery of the main member. The prepolymer can for example be supported by, e.g. impregnated into, an elastic support which is stretched over the heat-recoverable main member and which recovers towards a relaxed condition during heat-recovery of the main member. The treatment to effect polymerization can for example be to apply (e.g. spray) a chemical reagent, preferably water, and optionaUy a catalyst, to the prepolymer, or to expose the prepolymer to a catalyst and/or radiation which wUl effect polymerization thereof. When applied after recovery of the main member, the water or other chemical reagent can also serve to cool the heat-recovered cast. Particularly preferred prepolymers are polyurethane polymers which can be polymerized by the addition of water, and which typically are reaction mixtures of at least one polyol with a molar excess of at least one polyisocyanate so that the reaction mixture contains free isocyanate groups, generally 4 to 30%, preferably at least 5%, particularly at least 8%, free isocyanate groups. Suitable polyurethane prepolymers are disclosed, for example, in the documents incorporated herein by reference, and often include additional ingredients such as stabiUzers (e.g. benzoyl chloride), anti foaming agents (e.g. polysiloxanes), viscosity modifiers, and catalysts (e.g. tertiary amines). We have found that casts with higher strengths are often obtained when the polymerization of the prepolymer takes place at the same time as the recovery of the main member. The heating which causes recovery of the main member increases the rate of polymerization and reduces the viscosity of the polymerization mix, which results in less foaming, as compared to a separate polymerization step after recovery of the main member. When the flexible component is part of the heat-recoverable cast, it is important to store the cast under conditions which prevent the flexible component from becoming inflexible, for example in a moisture-impermeable envelope. When the reinforcing component is applied to the cast after it has recovered, it is not necessary that the reinforcing component be one which does not impede recovery. Thus the flexible component can for example comprise a prepolymer as described above, and the prepolymer can optionally be coated onto or otherwise associated with a substrate, e.g. a knitted, woven or non-woven fabric or netting, a polymeric film, or reinforcing fibers, which, if present before recovery of the cast, would impede recovery of the cast. The substrate can for example be knitted or woven from glass fiber yams, polypropylene yams, or elastic yarns, or combinations thereof. When the reinforcing component is applied to the recovered cast, it is also possible for it to comprise a thermoplastic material, preferably a thermoplastic polymer, optionaUy coated onto or otherwise associated with a substrate, e.g. as just described for a prepolymer. Suitable thermoplastic materials include those already known for use as casting materials, including those disclosed in the documents incorporated herein by reference. A preferred material comprises polycaprolactone or a derivative thereof, optionally mixed with one or more other polymers. The thermoplastic material can be preheated and applied hot to the recovered cast, or laid onto, preferably wrapped around, the recovered cast and then heated in situ. The reinforcing component can also be a second heat-recoverable cast, for example a heat-recoverable cast according to the first preferred embodiment of the present invention but without the liner, or a heat-recoverable cast according to the second or third preferred embodiment of the present invention, or a heat-recoverable cast as disclosed in US Serial Nos. 07/875,776 and 08/092,351 and International Application No. PCT/US93/03962 incorporated by reference herein. The second heat-shrinkable cast reinforces all or selected parts of the cast which has already been applied. It can also be used to improve the appearance of the cast and/or to cover the ends of a liner which have been folded back over the ends of the recovered main member. For example the reinforcing component can be a Uttle shorter than the applied cast, so that it covers the extremities of the folded ends of the liner, but leaves a margin, e.g. of 0.5 to 2 inch. Preferably at least a part of the main member lies between the reinforcing component and the Umb to which the cast is appUed. The main member can then act as a barrier between the Umb and the reinforcing component, for example to provide a thermal barrier between the Umb and a hot thermoplastic reinforcing component, or to prevent or reduce contact between the limb (and any bandages or dressings on the limb), and water or other reagent appUed to harden a prepolymer. When a reinforcing component is used, the reinforcing component is selected so as to enhance the physical and/or esthetic properties of the main member. Preferably the presence of the reinforcing component results in a finished cast whose crush strength is at least 1.5 times, particularly at least 2 times, the crash strength of a finished cast which is identical, and has been treated identicaUy, except that it does not include the reinforcing component. Indeed the reinforcing component can supply almost any proportion of the crash strength of the finished cast. For example, the heat-softenable casting polymer can be used in an amount which is sufficient to maintain the support in its elastically deformed state but which makes Uttle contribution to the strength of the finished cast. For example, the finished cast can have a crash strength which is more than 5 times, even more than 10 times, the crash strength of a finished cast which is identical except that it does not include the reinforcing component In this embodiment of the invention, the main member can act principaUy as a form which, after it has molded to the shape of the Umb, distributes the forces of the reinforcing component, particularly when the reinforcing component is supported on a sheet or tape, e.g. an elastic sheet or tape, which is wrapped around the recovered main member, and thus helps to ensure that no undue pressure is exerted on the Limb. Referring now to the drawings, Figures 1 and 2 are diagrammatic longitudinal and transverse cross-sections of a cast according to the invention which includes a heat- recoverable main member 1 and a padded stockinette Uner 2. The main member comprises multiple wraps (usuaUy 2 or 3) of the support, which is held in an elastically deformed condition by the casting composition. The ends of the liner 2 are folded back over the ends of the main member. Figure 3 is a diagrammatic plan view of a flattened heat-recoverable main member 1 which is suitable for use as an arm cast. A main member in the form of a cylinder has been flattened and then cut so as to produce a thumb hole 11 of diameter b at an axial distance a from one comer of the member. In addition, starting at a radial distance c from the same comer and ending at an axial distance d below the opposite comer, the end of the cyUnder has been cut off along Une 12, so that the member will conform better to the palmer creases of the hand. The invention is iUustrated by the following Examples. EXAMPLES Examples 1-15 In Examples 1 to 15, the support was made from an elasticaUy extensible fabric which is ava able from CaroUna Narrow Fabrics (Winston Salem, North Carolina, USA). The fabric is a three bar knitted warp fabric with ECDE 75 1/0 Z glass fiber yam in the first and second bars and a natural rubber yam in the third bar. It has a density (unstretched) of 800 + 100 g/m 2 and wiU return to substantially its original length if stretched by up to about 2.5 times its original length. The Uner is made from a padded stockinette having a flattened width of about 9 cm (i.e. a diameter of about 5.75 cm) which is available from Smith and Nephew Casting (Menomonee Falls, Wisconsin, USA) under the trade name Protouch One-Step and which is a cotton/spandex stockinette with an adhesively bonded polyester padding of low density which can be stretched by the stockinette without tearing. The polyurethane prepolymer compositions A and B contained the ingredients and amounts thereof (in grams) set out in the table below. Ingredients A B Isonate 143L 200 63 Pluracol P1010 188 19 Poly G 36-232 - 13.5 DABCO 6 2 Benzoyl chloride 0.2 0.1 Polydimethyl sUoxane 0.5 0.3 Isonate 143L is avaUable from Dow Chemical (Midland, Michigan, USA) and is methylene diphenylene dusocyanate and oUgomers thereof. Pluracol PI 010 is available from BASF Performance Chemicals (Parsippany, New Jersey, USA) and is polyethylene glycol. Poly G 36-232 is available from OUn Chemicals (Cheshire, Connecticut, USA) and is a polyether polyol. DABCO is avaUable from Air Products and Chemicals (AUentown, Pennsylvania, USA) and is triethylene diamine; it is a catalyst for the polymerization of Isonate 143L and Pluracol P1010. An altemative catalyst is DMDEE (2,2' dimorpholinodiethyl ether), which is avaUable from Texaco Chemicals (Houston, Texas, USA). Benzoyl chloride is an inhibitor. Polydimethyl siloxane is an antifoaming agent which is avaUable from Dow Coming (Midland, Michigan, USA) or from Huls America (Bristol, Pennsylvania, USA). Example 1 The casting composition used in Example 1 was a blend of about 80% of an SCC polymer having a T m of about 50°C and about 20% of an ethylene/vinyl acetate copolymer 0 V A) which is avaUable from duPont (Wilmington, Delaware, USA) under the trade name Elvax 210, is reported to contain about 28% vinyl acetate and to have a softening point of about 90°C. The blend has a molecular weight of about 200,000. The SCC copolymer had a molecular weight of about 220,000 and contained units derived from about 68% of dodecyl acrylate (C22A), about 4% acrylic acid (AA), and about 28% of styrene (STY). The blend was made by the foUowing procedure. C22A (68 parts), STY (28 parts), AA (4 parts) and dodecane thiol (0.04 parts) were mixed. 20 parts of the mixture were heated to about 120°C. The remaining 80 parts were mixed with t-amyl peroxy-2-ethyl hexanoate (0.5 part) and added over 90 minutes, maintaining the reaction mixture at 120°C. The temperature was raised to 140°C over a period of about 45 minutes, whUe adding t-amyl peroxy benzoate (0.5 part). The temperature was maintained at 140°C for a further 2 hours. EVA (25 parts) and butylated hydroxytoluene (0.3 part) were then added, and the mixture maintained at 40°C for a further 1-2 hours, with stirring. The blend was then cooled. The casting composition was heated to a temperature of about 100°C and was then melt coated onto a length of the support fabric, about 11.4 inch (28.8 cm) long and about 12 inch (30 cm) wide. The coated fabric was maintained at a temperature of about 100°C for about 4 hours to ensure that the support was thoroughly impregnated by the casting composition, and was then cooled. The coated fabric was reheated by means of a hot air gun to a temperature of about 90°C, stretched to about 2.5 times its original length, and cooled in the stretched state. The stretched fabric was about 28.5 inch (about 72 cm) long and about 12 inch (36 cm) wide, had an open structure with a plurality of apertures each having an area of about 0.02 cm 2 , and had an AFP of about 15.5%. The cooled, stretched, coated fabric was wrapped three times around a metal mandrel having a circumference of about 9.5 inch (about 24 cm), i.e. a diameter of about 3 inch (about 7 cm), and the outer wrapped end was secured to the layer below with a polyamide hot melt adhesive. The composite structure was removed from the mandrel. It had an AFP of about 7%. It was flattened and then cut to a shape as shown in Figure 3 (in which the outer edges of the portions removed are shown by the dotted lines) and having dimensions a, b, c and d approximately as follows: a, 4 cm; b, 3.8 cm; c, 3 cm; and d, 2 cm. The composite structure was restored to a generaUy cylindrical shape and a length of the liner fabric was placed inside it The liner fabric was about 15 inch (38 cm) long, and had a hole about 0.4 inch (1 cm) in diameter punched in it, the center of the hole being about 2.4 inch (about 6 cm) from one end. The centers of the holes in the heat- recoverable main member and the Uner were approximately aUgned, and the ends of the Uner were then stretched radiaUy and folded back over the ends of the main member. The resulting orthopedic cast could be flattened for storage purposes, and then restored to a generaUy cyUndrical shape before use. The cast (after being restored to a generaUy cylindrical shape) was slipped over a person's hand, wrist and forearm, with the thumb through the holes in the liner and main member, and with the angled end parallel to the palmer creases of the hand. The folded ends of the Uner were unfolded over the person's arm and hand. The heat-recoverable main member was then heated with a hot air gun to soften the casting composition and cause recovery of the cast around the wrist and forearm. This took about 2-5 minutes. The the Uner protected the patient from being burned by the hot air and the heated cast. After the cast had cooled, the ends of the liner were folded back over the cast, thus padding its edges. Example 2 Example 1 was repeated except that the casting composition was a polycaprolactone composition which is avaUable from Solvay Interox Chemicals (Warrington, Great Britain) under the trade name CAPA 640, and which has a T m of about 57°C and a reported molecular weight of about 37,000. The casts produced in Examples 1 and 2 had similar crash strengths (about 50 lb), but the adhesion between the layers was better in Example 2 than in Example 1. We have found that if the amount of EVA used in Example 1 is increased to about 40%, or if an EVA of higher molecular weight (e.g. Elvax 240) is used, the adhesion between the layers improves. Example 3 A cooled, stretched, coated fabric was made as in Example 1. A length of the fabric about 4 inch (10 cm wide) was wrapped twice around a metal mandrel having a circumference of about 24 cm, i.e. a diameter of about 7.6 cm, and the outer wrapped end was secured to the layer below with a polyamide hot melt adhesive. The composite structure was removed from the mandrel, placed over a second metal mandrel having a circumference of about 19 cm, i.e. a diameter of about 6 cm, and fuUy shrunk down onto the second mandrel, using a hot air gun. Its weight was about 25 g. Example 4 Example 3 was repeated, and the recovered cast, stiU on the mandrel, was coated with about 10 g of prepolymer composition A. The coating was then sprayed with water, and as a result polymerized, with foaming. The resulting cooled product had a substantially greater crash strength than the product of Example 3. Example 5 Example 3 was repeated except that before the composite stracture was shrunk down onto the second mandrel, it was coated with about 10 g of prepolymer composition A. Just before using the heat gun to shrink the composite structure, the prepolymer layer was sprayed with water. Application of the hot air gun resulted in simultaneous shrinkage of the composite structure and polymerization of the prepolymer. The polymerization mix foamed less and had a lower viscosity during the polymerization than in Example 4. The resulting cooled product had a substantially greater crash strength than the product of Example 4. Example 6 Example 3 was repeated except that the second mandrel had a circumference of about 14 cm, i.e. a diameter of about 4.5 cm. Example 7 Example 6 was repeated, and the recovered cast, stiU on the second mandrel, was coated with about 10 g of prepolymer composition B. The coating was then sprayed with water, and as a result polymerized, with foaming. Example 8 Example 6 was repeated except that before the composite stracture was shrank down onto the second mandrel, it was coated with about 10 g of prepolymer mixture composition B. Just before using the heat gun to shrink the composite stracture, the prepolymer layer was sprayed with water. Application of the hot air gun resulted in simultaneous shrinkage of the composite structure and polymerization of the prepolymer. The polymerization mix foamed less and had a lower viscosity during the polymerization than in Example 7. Example 9 Example 8 was repeated, taking particular care to ensure a uniform coating of the prepolymer composition. Example 10 Example 6 was repeated except that a film of the SCC/EVA casting composition, about 0.024 inch (about 0.6 mm) thick, was placed between the wraps of cooled, stretched, coated fabric before the composite structure was recovered by heating. The crush strengths of the products obtained in Examples 7-10 are shown below. Example No. 6 7 8 9 10 Crash Strength (lb) 1.7 15.2 14.4 26.2 8.1 Example 11 The procedure of Example 1 was foUowed up to the stage at which the composite stracture was removed from the mandrel. A piece of the support fabric (19.2 x 30 cm) impregnated with prepolymer composition B (45% of total weight), was formed into a tube using a polyamide hot melt adhesive. The tube was stretched and fitted over the composite stracture. The resulting assembly was placed over a mandrel (diameter about 4.5 cm) and then heated with a hot air gun at about 70°C for about 5 minutes so that the cast recovered and conformed to the mandrel. Water was then sprayed onto the cast, causing polymerization of the prepolymer. The finished cast had a substantially greater crash strength than the product of Example 1. Example 12 Two identical composite structures were made by the procedure of Example 1 except that the expanded support fabric was 48 x 10 cm and was wrapped twice around the 24 cm mandrel. The first stracture was placed over a mandrel (diameter 4.5 cm); and heated in an oven at about 70°C for about 5 minutes so that it recovered. The second structure was then placed over the first, and heated in an oven at about 70°C for about 5 minutes so that it recovered. Example 13 The procedure of Example 12 was foUowed except that a single composite structure was prepared and recovered. Examples 14-15 The procedures of Examples 12 and 13, respectively, were foUowed, except that the casting composition was CAPA 640 as in Example 2. The crush strengths of the recovered casts in Examples 12-15 are given in the table below. Example No. 12 13 14 15 Crush Strength (lb) 50 9.6 69 26 Examples 16-22 . Examples 16-22 are summarized in the Table below and Ulustrate the improved results which can be obtained by using more open knitted fabric supports. Example 16 shows the results obtained with a knitted fabric which is not in accordance with the third aspect of the invention because the openings in it are too numerous and too small. In each of Examples 16-22, an elastic knitted fabric was prepared on a three-bar Raschel knitting machine, using the number of needles/inch, courses/inch and fabric wales shown in the Table. In each Example, Bar 2 was a fiberglass yam (diameter about 0.0156 inch) available from PPG Industries Inc. under the trade name ECDE 37 1/0 (abbreviated to FG37 in the Table). In Examples 17, 19, 20 and 21, Bar 1 was the same as Bar 2. In Examples 16 and 18, Bar 1 was a fiberglass yam (diameter about 0.0106 inch) avaUable from PPG Industries Inc.under the trade name ECDE 75 1/0 (abbreviated to FG75 in the Table). In each of the Examples, Bar 3 was a natural rabber monofilament yam which had a diameter of about 0.0165 inch (0.04 cm) in Example 16 (abbreviated to R60 in the Table) and about 0.019 inch (0.05 cm) in Examples 17-22 (abbreviated to R50 in the Table); both yams are avaUable from Globe Rubber Co. under the trade name GM9. The fabric, as made and fuUy relaxed, was examined to determine its density, its thickness, its power, and the number of holes per inch 2 ; the results are shown in the Table. In each of the Examples, the fabric was stretched by about 150% in the longitudinal direction, i.e. to about 2.5 times its original length (the transverse dimension changes by less than 10%), and whUe stretched was melt-coated with a polycaprolactone (PCL) composition which is available from Solvay Interox Chemicals (Warrington, Great Britain) under the trade name CAPA 640, and which has a Tm of about 57°C and a reported molecular weight of about 37,000. The stretched, coated fabric was maintained at a temperature of about 110°C for a time sufficient to ensure that the fabric was thoroughly impregnated by the PCL, and was then cooled in the stretched state. The number of holes per square inch, the average hole size, and the AFP, of the cooled, stretched, coated fabric were measured, and the results are shown in the Table under the heading "ready-for-use". A first sample of each fabric was recovered 20%, and the average size of the holes and the AFP were measured. The results are shown in the Table under the heading "recovered 20%". A second sample of the coated fabric about 10 cm wide was wrapped 2, 3 or 4 times (as reported in the Table) around a first metal mandrel having a circumference of 24 cm, and the outer wrapped end was secured to the layer below with a polyamide hot melt adhesive. The wrapped fabric was removed from the first mandrel, placed over a second metal mandrel having a circumference of 14 cm, and then heated with a hot air gun until the PCL softened, permitting the fabric to recover against the second mandrel and causing the wrapped fabric layers to bond to each other. In one part of Example 16, a first sample of the coated stretched fabric was wrapped twice around the first mandrel, and then heated and recovered around the second mandrel; and after the first sample had cooled, a second sample of coated stretched fabric was wrapped twice around the first mandrel, removed from the first mandrel, placed over the second mandrel and the first sample recovered over the second mandrel, and then heated and recovered. After cooling, the recovered product was removed from the second mandrel and tested for crash strength. The crash strengths are reported in the Table. TABLE

Claims: CLAIMS 1. An article which is suitable for use as an orthopedic cast which comprises ( 1 ) a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which (i) comprises a casting polymer having a transition point T s , (u) contacts the support and maintains it in an elastically stretched condition, and (ui), when the cast is heated to a temperature above T s after it has been placed around a limb, softens and permits shrinkage of the heat-shrinkable member towards the limb, and (2) a Uner which is secured to the inside of the main member and which, when the cast is heated after it has been placed around a limb, provides a thermal barrier between the Umb and at least part of the main member. 2. An article according to claim 1 wherein the liner comprises a tube of elastically stretched stockinette fabric. 3. An article according to claim 1 or 2 wherein the Uner comprises a padding material which is compressed when the main member is shrank by heating the cast after it has been placed around a Umb. 4. An article according to any one of the preceding claims wherein the liner has an air flow permeabiUty of less than 25%. 5. An article according to any one of the preceding claims wherein the heat-shrinkable main member has a plurality of apertures through its thickness, each of the apertures having an area of 0.01 to 0.12 cm 2 , and the liner has an air flow permeabUity which is less than 0.75 times the air flow permeabiUty of the heat-shrinkable main member. 6. An article which is suitable for use as an orthopedic cast and which comprises (1) a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which (i) comprises a casting polymer having a transition point T s , (U) contacts the support and maintains it in an elastically stretched condition, and (ui), when the cast is heated to a temperature above T s after it has been placed around a limb, softens and permits shrinkage of the heat-recoverable member towards the limb, and (2) a flexible reinforcing component which is provided on at least part of the main member and which can be subjected to a treatment which wiU reduce its flexibiUty. 7. An article according to claim 6 wherein the reinforcing component is precursor for a crosslinked polymer, preferably a water-hardenable precursor for a polyurethane. 8. A heat-shrinkable article which (1) is suitable for use as an orthopedic cast or can be converted into an article suitable for use as an orthopedic cast; (2) comprises (a) a knitted fabric support which (i) is in an elastically stretched condition, (U) comprises at least one elasticaUy stretched yam and at least one relatively inextensible yam, and (ni) when on its own in a fully relaxed state, has at most 300 holes per inch 2 (at most 45 holes per cm 2 ); and (b) a solid casting composition which (i) comprises a casting polymer having a transition point, T s , which is above 40°C, and (U) contacts the support and maintains it in the elastically stretched condition, but does not fiU the holes of the support; and (3) when heated above T s in the absence of any restraint, shrinks so that at least one dimension of the article decreases from a first value x to a second value y which is at most 0.95x, said shrinkage being due at least in part to elastic shrinkage of the elasticaUy stretched yam. 9. An article according to claim 8 wherein the support, on its own in a fuUy relaxed state, has 50 to 250, preferably 80 to 220, holes per inch 2 (8 to 40, preferably 12 to 34, holes per cm 2 ). 10. An article according to claim 8 or 9 which has 20 to 100, preferably 30 to 60, holes per inch 2 (3 to 15, preferably 5 to 10, holes per cm 2 ). 11. An article according to claim 8, 9 or 10 wherein the average size of the holes is 0.03 to 0.12, preferably 0.03 to 0.09, cm 2 . 12. A heat-shrinkable article which is suitable for use as an orthopedic cast or which can be converted into an orthopedic cast, and which comprises (a) an elastically stretched support, and (b) a casting composition which (i) comprises a casting polymer having a transition point, T s , which is at least 55°C, (u) contacts the support and maintains it in an elasticaUy stretched condition, and (iii) when the cast is heated to a temperature above T s after it has been placed around a limb, softens and permits shrinkage of the heat-shrinkable member towards the limb. 13. An article according to any one of the preceding claims wherein the casting polymer is polycaprolactone or another crystalUne polymer having a melting point, T m , from45° to 85°C. 14. An article according to any one of the preceding claims wherein the support comprises at least one yam composed of an elastomer and at least one high strength inextensible yarn which is substantially free from permanent crimps. 15. An article according to any one of the preceding claims wherein the support is warp-knitted, preferably on a Raschel knitting machine. 16. An article according to any one of the preceding claims which, when heated above Ts in the absence of any restraint, shrinks so that at least one dimension of the article decreases from a first value x to a second value y which is at most 0.75x, the shrinkage being due at least in part to elastic shrinkage of elastically stretched yams in the support. 17. An article according to any one of the preceding claims which comprises a laminate of two or three supports, each maintained in an elasticaUy stretched condition by a solid casting composition. 18. A method of forming an orthopedic cast around a Umb, which method comprises (A) placing around the Umb an article as claimed in any one of the preceding claims which, when in position around the limb, has a closed cross-section, and (B) heating the article so as to soften the casting composition and cause shrinkage of the article towards the Umb. 19. A method according to claim 18 which includes the steps of (C) providing on at least a part of the main member a flexible reinforcing component which can be subjected to a treatment which will reduce its flexibiUty; and (D) subjecting the reinforcing component to a treatment which reduces its flexibiUty. 20. A method according to claim 19 wherein step (C) is carried out prior to step (B); step (P) is carried out simultaneously with step (B) or after step (B); and the reinforcing component is a water-hardenable polyurethane precursor. 21. A method of forming an orthopedic cast around a Umb, which method comprises (A) placing around the Umb an orthopedic cast which has a closed cross-section and which comprises a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which contacts the support and maintains it in an elasticaUy stretched condition; (B) heating the orthopedic cast so as to soften the casting composition and cause shrinkage of the heat-shrinkable member towards the Umb; (C) subjecting a flexible reinforcing component on at least part of the main member to a treatment which reduces its flexibiUty, said treatment being carried out during step (B), or after step (B), or both. 22. A method of forming an orthopedic cast around a Umb, which method comprises (A) placing around the Umb an orthopedic cast which has a closed cross- section and which comprises a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which contacts the support and maintains it in an elasticaUy stretched condition; (B) placing a Uner between the cast and the limb; and (C) heating the orthopedic cast so as to soften the casting composition and cause shrinkage of the heat-shrinkable member towards the limb. 23. A method according to claim 22 wherein the Uner is placed around the limb before the cast. 24. A method of making an orthopedic cast as defined in claim 6 or 7, which method comprises (A) providing an elasticaUy stretchable support; (B) contacting the support, while it is elasticaUy stretched, with a casting composition which comprises a casting polymer having a transition point T s and which is at a temperature above T s ; (C) cooling the casting composition to a temperature below T s to produce a heat-shrinkable main member wherein the casting composition maintains the support in an elastically stretched condition; and (D) providing on the main member a flexible reinforcing component which can be subjected to a treatment which wiU reduce its flexibiUty. 25. A method of making a removable splint which comprises (A) placing around the Umb an orthopedic cast which has a closed cross- section and which comprises a heat-shrinkable main member which comprises (a) an elastically stretched support, and (b) a casting composition which contacts the support and maintains it in an elasticaUy stretched condition; (B) heating the orthopedic cast so as to soften the casting composition and cause shrinkage of the heat-shrinkable member towards the Umb; (C) after the cast has cooled, dividing it along one or more Unes so that it can be removed from the limb; and (D) securing fasteners to the cast so that the cast after it has been removed from the Umb, can be replaced and secured around the Umb. 26 A removable splint which comprises (1) a polymeric cast which is divided along at least one line so that it can be placed over and removed from a Umb, said cast comprising a fabric support and thermoplastic polymer contacting the support, and (2) fasteners which can be used to secure the cast around a limb. 27. An article which is suitable for use as an orthopedic casting tape and which comprises (a) a knitted fabric support which (i) comprises at least one elasticaUy extensible yam and at least one relatively inextensible yam, (u) when on its own in a fully relaxed state, has at most 300 holes per inch 2 (at most 45 holes per cm 2 ) and can be elasticaUy extended in a lengthwise direction to an elastic Umit at which its length is between 1.15 times and 1.4 times its fully relaxed length, and (b) a polymeric casting composition which contacts the support and which comprises a curable precursor for a polymer. 28. A method of forming an orthopedic cast around a Umb which comprises (A) wrapping around the limb a casting tape according to claim 27 while the casting composition is in a state which permits elastic extension of the support, and (B) treating the casting composition so that, after the casting tape has been wrapped around the Umb, the composition hardens to form a relatively rigid cast

Inventors: BITLER STEVEN P, DAHLEN BURTON L, GREENE LAWRENCE C, LARSON ANDREW W, TAFT DAVID D, BITLER, STEVEN, P., DAHLEN, BURTON, L., GREENE, LAWRENCE, C., LARSON, ANDREW, W., TAFT, DAVID, D.
Applicants: BITLER STEVEN P, DAHLEN BURTON L, GREENE LAWRENCE C, LANDEC CORP, LARSON ANDREW W, TAFT DAVID D, BITLER, STEVEN, P., DAHLEN, BURTON, L., GREENE, LAWRENCE, C., LANDEC CORPORATION, LARSON, ANDREW, W., TAFT, DAVID, D.
Application year: 1994
Main classification: A61F13
IPC codes: A61F5, A61F13, A61L15